/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.util;


/**
 * A special {@link Error} which is used to signal some state or request by throwing it. {@link
 * Signal} has an empty stack trace and has no cause to save the instantiation overhead.
 */
public final class Signal extends Error implements Constant<Signal> {

  private static final long serialVersionUID = -221145131122459977L;

  private static final ConstantPool<Signal> pool = new ConstantPool<Signal>() {
    @Override
    protected Signal newConstant(int id, String name) {
      return new Signal(id, name);
    }
  };

  /**
   * Returns the {@link Signal} of the specified name.
   */
  public static Signal valueOf(String name) {
    return pool.valueOf(name);
  }

  /**
   * Shortcut of {@link #valueOf(String) valueOf(firstNameComponent.getName() + "#" +
   * secondNameComponent)}.
   */
  public static Signal valueOf(Class<?> firstNameComponent, String secondNameComponent) {
    return pool.valueOf(firstNameComponent, secondNameComponent);
  }

  private final SignalConstant constant;

  /**
   * Creates a new {@link Signal} with the specified {@code name}.
   */
  private Signal(int id, String name) {
    constant = new SignalConstant(id, name);
  }

  /**
   * Check if the given {@link Signal} is the same as this instance. If not an {@link
   * IllegalStateException} will be thrown.
   */
  public void expect(Signal signal) {
    if (this != signal) {
      throw new IllegalStateException("unexpected signal: " + signal);
    }
  }

  @Override
  public Throwable initCause(Throwable cause) {
    return this;
  }

  @Override
  public Throwable fillInStackTrace() {
    return this;
  }

  @Override
  public int id() {
    return constant.id();
  }

  @Override
  public String name() {
    return constant.name();
  }

  @Override
  public boolean equals(Object obj) {
    return this == obj;
  }

  @Override
  public int hashCode() {
    return System.identityHashCode(this);
  }

  @Override
  public int compareTo(Signal other) {
    if (this == other) {
      return 0;
    }

    return constant.compareTo(other.constant);
  }

  @Override
  public String toString() {
    return name();
  }

  private static final class SignalConstant extends AbstractConstant<SignalConstant> {

    SignalConstant(int id, String name) {
      super(id, name);
    }
  }
}
